The largest, heaviest, and most costly part of an RF system is the transmitter. This part also draws the most prime power and requires the most cooling-factors which further influence the size, weight and cost of a system. The design of the transmitter is very strongly affected by the design of the RF tube or source. Therefore, RF-tube development has a long and varied history. These development efforts have produced the lighthouse tube, the pencil tube, the disk-sealed tetrode, the resnatron, the B-K (Barkhausen and Kurtz) tube, the klystron, the reflexklystron, the magnetron, the traveling-wave tube, the backward-wave oscillator, the platinatron, the amplitron, the stabilatron, the helitron, the spinatron, the crestatron, the larmatron, the tornadotron, the laddertron, the gyrotron, the cyclotron maser, the ledatron, and the free electron laser; to name a few.
The concept of energy conversion between the electron beam and electromagneic waves and principles of operation of these devices are discussed by T Koryu Ishii in "MICROWAVE ENGINEERING", The Ronald Press Co. New York, 1966; Kenneth J. Button in "Infrared and Millimeter Waves", Academic Press, New York, 1979; and Merrill I. Skolnik in "Radar Handbook", McGraw-Hill Book Co., New York 1970.
Most of these are relatively inflexible special-purpose devices and many of them require the production and control of high voltage electron beams, magnetic guide fields, and in some cases magnetic wiggler fields. Others are crossfield devices where the electric and magnetic fields are perpendicular to each other with the magnetic field being used to cause the electron beam to curve or rotate. In some cases, as with the traveling-wave tube the backward-wave oscillator, the cyclotron maser, and the free electron laser, it is necessary to establish and maintain a phase match between electromagnetic radiation and the electron beam. In all cases, they are complex and they are sometimes difficult to utilize.